public class Test {
    public static void main(String[] args) {
        BinarySearchTree binarySearchTree = new BinarySearchTree();
        binarySearchTree.insert(18);
        binarySearchTree.insert(10);
        binarySearchTree.insert(21);
        binarySearchTree.insert(9);
        binarySearchTree.insert(15);
        binarySearchTree.remove(18);
    }
}
